1. Field of the Invention
The present invention relates to systems and methods for receiving layered modulation signals, particularly in a direct satellite broadcast system.
2. Description of the Related Art
Digital signal communication systems have been used in various fields, including digital TV signal transmission, either terrestrial or satellite. As the various digital signal communication systems and services evolve, there is a burgeoning demand for increased data throughput and added services.
It has been proposed that a layered modulation signal, transmitting coherently or non-coherently both upper and lower layer signals, can be employed to meet these needs and more. Such layered modulation systems allow higher information throughput, with and without backward compatibility. When backward compatibility is not required (such as with an entirely new system), layered modulation can still be advantageous because it requires a TWTA peak power significantly lower than that for a conventional 8 PSK or 16 QAM modulation format for a given throughput.
However, to receive such layered modulation signals requires reconstruction of the upper layer signals to remove them from the total signal for lower layer signal processing to occur. Further, the performance of lower layer demodulation depends on the cancellation accuracy. The reconstructed signal should optimally match the received signal in overall amplitude and phase. Therefore, amplitude and phase errors in the reconstructed signal at the point of signal cancellation need to be estimated.
Accordingly, there is a need for systems and methods for amplitude and phase matching of the received signal with the reconstructed signal in a communication system using layered modulation. The present invention meets these needs.